Proton Transport and Chloride Cells in the Gill of Rainbow Trout (Oncorhynchus mykiss)

Particulate preparations from freshwater rainbow trout (Oncorhynchus mykiss) gill homogenates contain an active magnesium ion activated ATPase that transports protons into the-vesicles. Oligomycin at a concentration of 20 mug.mL-1 had little effect on the proton transport, which was completely inhibited by N-ethylmaleimide. This inhibition was partly counteracted by dithiothreitol. Proton transport in freshwater trout gill submitochondrial particles was completely inhibited by oligomycin. When freshwater trout were kept for 40 min in water equilibrated with air containing 5% carbon dioxide, their gill lamellar epithelium contained many cells densely covered with erect microvilli. After changing to water bubbled with room air, the cells rapidly lost their microvilli. Control fish that were killed immediately after removal from the storage tank also had microvilli, but less erect and fewer in number. Labelled latex microspheres and dextran were used as markers for external medium uptake into gill epithelial cells. The fish were pretreated by bubbling the water by air containing 5% carbon dioxide, and the uptake took place when the water was bubbled with room air.